Records for configuring Remote about acid-state

[nikita-volkov]

TLDR completely, as suggested )
I actually have something "in the spirit" already implemented in private projects. Haven't worked on integrating it into the acid-state yet though. The configurations are separated for client and server, the code explains why. Besides solving the configuration issues it also abstracts over connecting to local or remote server or running the server itself with openExisting.
@lemmih what do you think about that?

startServer 
  :: IsAcidic a
  => Either (Int, Set ByteString) FilePath 
  -- ^ Port and secrets or a socket file
  -> AcidState a
  -- ^ State
  -> IO ()
startServer options acid = case options of
  Left (port, secrets) -> do
    Acid.acidServer 
      (Acid.sharedSecretCheck secrets) 
      (Network.PortNumber $ fromIntegral port) 
      acid
  Right socket -> do
    Acid.acidServer 
      Acid.skipAuthenticationCheck
      (Network.UnixSocket $ FilePath.encodeString socket) 
      acid



data URL 
  = Socket FilePath
  -- ^ A path to a socket file
  | Host Text Int (Maybe ByteString) 
  -- ^ Host, port and secret
  | Path FilePath
  -- ^ A path to local state
  | Name Text 
  -- ^ A name of state located under standard local directory
  deriving (Eq, Ord, Show)

-- | Open an existing state by "URL".
-- TODO: handle connection failure and probably return 'Either'.
openExisting :: IsAcidic a => URL -> IO (AcidState a)
openExisting url = case url of
  Host host port (Just secret) -> 
    Acid.openRemoteState 
      (Acid.sharedSecretPerform secret) 
      (Text.unpack host)
      (Network.PortNumber $ fromIntegral port)
  Host host port _ -> 
    Acid.openRemoteState 
      Acid.skipAuthenticationPerform 
      (Text.unpack host)
      (Network.PortNumber $ fromIntegral port)
  Socket path -> do
    path' <- FilePath.resolve path
    Acid.openRemoteState
      Acid.skipAuthenticationPerform 
      ""
      (Network.UnixSocket $ FilePath.encodeString path')
  Path path -> do
    path' <- FilePath.resolve path
    Acid.openLocalStateFrom (FilePath.encodeString $ path') $
      error $ "No initialized local state found at following path: " <> FilePath.encodeString path
  Name name -> do
    home <- FilePath.getHomeDirectory
    let path = home <> ".acid-databases" <> FilePath.fromText name
    openLocalStateFrom (FilePath.encodeString path) $
      error $ "No initialized local state found under following name: " <> Text.unpack name

[lemmih]

I defer all judgement regarding the remote backend to @stepcut.

[dag]

@nikita-volkov Your ideas inspired me to rethink some things, so I think I have an API I'm satisfied with now.

[stepcut]

However, the fact that sharedSecretCheck takes a set of secrets suggests that acid-state wants to support more complex setups where you have multiple clients connecting from multiple systems. In this type of use, I think separate configurations better reflect reality, at the expense of complicating the simpler cases a bit.

Correct -- it is setup so that there could be multiple clients and then you could revoke access to one of them. It is also setup so that other authentication schemes could be used besides shared secrets.

Although not currently supported, it could also be nice if there were two permission levels -- read vs read/write. Or perhaps a scheme where each client has a whitelist of which specific methods they can invoke.